An interconnect system is a system by which information is communicated between distinct entities, such as between computer chips on a printed circuit board (PCB) or multi-chip module (MCM). The term “interconnect”, when used as a noun, refers to the medium by which the information is communicated. An interconnect may be an electrical connection, such as a wire or signal trace on a PCB or MCM, an optical connection, such as an optical fiber, or a wireless connection, such as a radio-frequency link. As used herein, however, the term “interconnect system” refers to a system that communicates information or data via a physical, electrical connection.
A binary interconnect system transmits information by imposing one of two possible states onto each interconnect. For example, a binary interconnect system may impose one of two voltages onto each interconnect, or may impose current through the interconnect, where the current is one of two levels or one of two directions. In a binary interconnect system, the two possible states may represent two logical values, e.g., 0 and 1. A multi-mode interconnect (MMI) system codes bits onto a set of levels distributed through a multi-channel interconnection, such as a wire bundle containing more than 2 wires.
However, there are disadvantages associated with multi-mode interconnect systems. One problem is that signals that travel down a real-world (not simulated) interconnect will suffer some signal loss. For example, a binary system which uses 0 volts to represent a logic 0 and 5 volts to represent a logic 1 may apply 5 volts to one end of a long interconnect, but due to impedance losses, the voltage at the other end of the long interconnect may be less than 5 volts, e.g., 3 volts, which is a 2-volt drop. A conventional solution to this kind of signal loss is to overdrive the source end of the interconnect, e.g., to 7 volts, so that even with the 2-volt drop across the interconnect, the voltage at the destination end of the interconnect is still 5 volts, i.e., still identifiable as a logic 1.
However, the amount of loss suffered may vary according to the frequency at which the signal is transmitted. For example, a 0-to-5 transition may have a short transition time at the driven end of the interconnect but a long transition time at the other end of the interconnect, with the result that the maximum rate at which the driven end of the interconnect may change state, e.g., the maximum frequency or data rate, is limited by the time that the signal takes to transition at the other end. A conventional solution to this kind of signal loss is to change the shape of the waveform at the source end of the interconnect, so that by the time the waveform arrives at the destination end of the interconnect, the shape of the waveform is such that the intended information can be identified or extracted. For example, if the slope of the rising edge of the signal applied to the source end of the interconnect can be made to be very steep, then by the time the signal arrives at the destination end, the transition time of the resulting waveform is not so long as to limit the frequency or data rate.
Although the techniques described above may work for binary interconnect systems, there are problems that arise when these techniques are applied to multi-mode interconnect systems which use a code word transmitted on a wire bundle to represent discrete data values. Conventional means to provide equalization require that succeeding bits get changed based on preceding values. This does not work for multi-mode interconnect systems, because multi-mode interconnect systems require a specific code word for each bit interval. For example, overdriving the voltage applied to the source end of the interconnect, as described in the first example, above, or changing the waveform to have a sharper slope, as described in the second example, above, both have the potential to change the value of the signal received by too much or too little, with the result that one or more of the received signals is incorrectly perceived to be a different voltage level than was intended, causing the code word that is received to be different from the code word that was transmitted.
Accordingly, in light of these disadvantages associated with conventional telecommunication networks that support mobile subscribers, there exists a need for systems, methods, and computer readable media for fractional pre-emphasis of multi-mode interconnect.